1. Field of the Invention
This invention relates to the drilling art and to the means in which the drill bit is advanced in a hole.
More particularly, this invention relates to a means to enhance the drilling rate of a conventional rock bit by utilizing at least one cavitation inducing nozzle in combination with conventional nozzles to induce cross-flow of drilling mud near the rock-tooth interface for more rapid removal of cuttings from the hole bottom.
2. Description of the Prior Art
The use of the cavitation phenomenon to erode solid material is taught in U.S. Pat. Nos. 3,528,704 and 3,713,699. The earlier '704 patent describes a method for utilizing the normally destructive forces of cavitation to provide an erosion effect for accomplishing drilling, boring and like functions of solids which comprise forming a fluid jet by directing the fluid through a restricted orifice at speeds sufficient to generate vapor-filled bubbles in the jet and impinging the jet against the solid at a distance from the orifice where the vapor bubbles collapse or implode.
The patent describes and illustrates fluid under pressure that is forced out of an exit opening which necks down from an upstream chamber. In most embodiments, a central concentric rod or pintle is introduced near the opening to induce cavitation as the liquid is forced out of the exit orifice. The resultant formation growth and collapse of vapor-filled cavities or "bubbles" in a flowing liquid that occurs at a level where local pressure is reduced below the vapor pressure of the liquid causes the erosion of the solid material. The implosion of the collapsing cavity happens with such violence it damages and erodes the material with which it comes into contact.
The later '699 prior art patent teaches a slight improvement in the destructive power of the cavitation phenomenon by surrounding the caviting jet with a liquid medium.
While the foregoing patents describe a means to excavate a hole, the cavitation erosion method is disadvantaged in that drilling rates are relatively slow when compared to the drilling rate of standard rock bits; such as, drag bits, one cone, or multi-cone rock bits.
It is known in the prior art to plug a nozzle opening in a rock bit opposite an opposing nozzle in the bit to induce cross-flow of liquid from one nozzle toward a plugged nozzle. Pressures, however, are generally constant in the hole bottom using this technique and the removal of rock chips is less effective.
The instant invention takes advantage of the pressure reducing characteristics of cavitating nozzle to induce cross-flow of drilling mud by placing a cavitating nozzle opposite a conventional nozzle. The mud passing through the conventional nozzle is at a higher pressure, hence the fluid moves toward the low pressure area, resulting in a cross-flow that rapidly removes the cuttings from the hole bottom.
The prior art heretofore described does not teach or suggest the combination of cavitating jets with conventional jets in rock bits.